The behavior of the honey bee in pollen collecting

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t% D

U. S. DEPARTMENT OF AGRICULTURE,
BUREAU OF ENTOMOLOGY— BULLETIN No. 121.

L. O. HOWARD, Entomologist and Chief of Bureau.

m THE BEHAVIOR OF THE HONEY BEE
IN POLLEN COLLECTING.

BY

D. B. CASTEEL, Ph. D.,

Collaborator and Adjunct Professor of Zoology,
University of Texas.

Issued December 31, 1912.

WASHINGTON:

GOVERNMENT PRINTING OFFICE.

1912.

U. S. DEPARTMENT OF AGRICULTURE,
BUREAU OF ENTOMOLOGY— BULLETIN No. 121.

L. O. HOWARD, Entomologist and Chief of Bureau.

THE BEHAVIOR OF THE HONEY BEE
IN POLLEN COLLECTING.

BY

D. B. CASTEEL, Ph. D.,

Collaborator and Adjunct Professor of Zoology,
University of Texas.

Issued December 31, 1912.

WASHINGTON:

GOVERNMENT PRINTING OFFICE,

1912,

BUREAU OF ENTOMOLOGY.

L. O. Howard, Entomologist and Chief of Bureau.

C. L. Marlatt, Entomologist and Acting Chief in Aosence of Chief.

It. S. Clifton, Executive Assistant.

W. F. Tastet, Chief Clerk.

F. H. Chittenden,^ charge of truck crop and stored product insect investigations.

A. D. Hopkins, in charge of forest bisect investigations.

TV. D. Hunter, in charge of southern field crop insect investigations.

F. M. "Webster, in charge of cereal and forage insect investigations.
A. L. Quaintance, in charge of deciduous fruit insect investigations.
E. F. Phillips, in charge of dee culture.

D. M. Rogers, in charge of preventing spread of moths, field work.
Rolla P. Currie, m charge of editorial work.
Mabel Colcord, in charge of library.

Investigations in Bee Culture.
E. F. Phillips, in charge.

G. F. White, J. A. Nelson, experts.

G. S. Demuth, A. H. McCray, N. E. McIndoo, apicultural assistants.
Pearle H. Garrison, preparator.
D. B. Casteel, colladorator.
2

LETTER OF TRANSMITTAL.

U. S. Department of Agriculture,

Bureau of Entomology,
Washington, D. C, September 23, 1912.
Sir: I have the honor to transmit herewith a manuscript entitled
" The Behavior of the Honey Bee in Pollen Collecting," by Dr. Dana
B. Casteel, of this bureau. The value of the honey bee in cross pol-
linating the flowers of fruit trees makes it desirable that exact infor-
mation be available concerning the actions of the bee when gathering
and manipulating the pollen. The results recorded in this manu-
script are also of value as studies in the behavior of the bee and will
prove interesting and valuable to the bee keeper. The work here
recorded was done by Dr. Casteel during the summers of 1911 and
1912 at the apiary of this bureau.

I recommend that this manuscript be published as Bulletin No. 121
of the Bureau of Entomology.

Eespectfully, L. O. Howard,

Entomologist and Chief of Bureau.
Hon. James Wilson,

Secretary of Agriculture.

CONTENTS.

Page.

Introduction 7

The structures concerned in the manipulation of pollen \ 7

The pollen supply 10

General statement of the pollen-collecting process 11

Action of the forelegs and mouthparts 13

Action of the middle legs 14

Action of the hind legs 16

Additional details of the basket-loading process 18

Pollen moistening 22

Storing pollen in the hive 29

Summary 31

Bibliography 33

Index 35

5

ILLUSTRATIONS

TEXT FIGURES.

Page.

Fig. 1. Left foreleg of a worker bee 8

2.. Left middle leg of a worker bee 9

3. Outer surface of the left hind leg of a worker bee '. 10

4. Inner surface of the left hind leg of a worker bee 11

5. A flying bee, showing the manner in which the forelegs and middle legs

manipulate pollen 14

6. A bee upon the wing, showing the position of the middle legs when they

touch and pat down the pollen masses 15

7. A bee upon the wing, showing the manner in which the hind legs are

held during the basket-loading process 17

8. The left hind legs of worker bees, showing the manner in which pollen

enters the basket 19

9. Inner surface of the right hind leg of a worker bee which bears a com-

plete load of pollen 22

6

THE BEHAVIOR OF THE HONEY BEE IN POLLEN COLLECTING.

INTRODUCTION.

While working upon the problem of wax-scale manipulation dur-
ing the summer of 1911 the writer became convinced that the so-
called wax shears or pinchers of the worker honey bee have nothing
whatever to do with the extraction of the wax scales from their
pockets, but rather that they are organs used in loading the pollen
from the pollen combs of the hind legs into the corbiculse or pollen
baskets (Casteel, 1912). Further observations made at that time dis-
closed the exact method by which the hind legs are instrumental in
the pollen-loading process and also the way in which the middle legs
aid the hind legs in patting down the pollen masses. During the
summer of 1912 additional information was secured, more particu-
larly that relating to the manner in which pollen is collected upon
the body and legs of the bee, how it is transferred to the hind legs,
how it is moistened, and finally the method by which it is stored in
the hive for future use. In the present paper a complete account will
be given of the history of the pollen from the time it leaves the flower
until it rests within the cells of the hive. The points of more par-
ticular interest in the description of pollen manipulation refer to
(1) the movements concerned in gathering the pollen from the
flowers upon the body and legs, (2) the method by which the baskets
of the hind legs receive the loads which they carry to the hive, and
(3) the manner in which the bee moistens pollen and renders it suf-
ficiently cohesive for packing and transportation.

THE STRUCTURES CONCERNED IN THE MANIPULATION OF

POLLEN.

The hairs which cover the body and appendages of the bee are of
the utmost importance in the process of pollen gathering. For the
purposes of this account these hairs may be classified roughly as
(1) branched hairs and (2) unbranched hairs, the latter including
both long, slender hairs and stiff, spinelike structures.

1 Of these two classes the branched hairs are the more numerous.
They make up the hairy coat of the head, thorax, and abdomen, with
the exception of short sensory spines, as those found upon the an-
tenna? and perhaps elsewhere, and the stiff unbranched hairs which

7

8

BEHAVIOB OF HONEY BEE IN POLLEN COLLECTING.

Trochanter-

Tibia

cover the surfaces of the compound eyes (Phillips, 1905). Branched
hairs are also found upon the legs ; more particularly upon the more
proximal segments. A typical branched hair is composed of a long-
slender main axis from which spring numerous short lateral barbs.
Grains of pollen are caught and held in the angles between the axis
and the barbs and between the barbs of contiguous hairs. The hairy
covering of the body and legs thus serves as a collecting surface upon
which pollen grains are temporarily retained and from which they
are later removed by the combing action of the brushes of the legs.
Although, as above noted, some unbranched hairs are located upon
the body of the bee, they occur in greatest numbers upon the more
distal segments of the appendages. They are quite diverse in form,
some being extremely long and slender, such as those which curve

over the pollen
jCoxa baskets , others

being stout and
stiff, as those
which form the
collecting brushes
and the pecten
spines.

The mouth-
parts of the bee
are also essential
to the proper col-
lection of pollen.
The mandibles
are used to scrape
over the anthers
of flowers, and
considerable pollen adheres to them and is later removed. The same
is true of the maxillae and tongue. From the mouth comes the fluid
by which the pollen grains are moistened.

The legs of the worker bee are especially adapted for pollen gath-
ering. Each leg bears a collecting brush, composed of stiff, un-
branched hairs set closely together. These brushes are located upon
the first or most proximal tarsal segment of the legs, known techni-
cally as the palmse of the forelegs and as the plantse of the middle
and hind pair. The brush of the foreleg is elongated and of slight
width (fig. 1), that of the middle leg broad and flat (fig. 2), while
the brush upon the planta of the hind leg is the broadest of all, and
is also the most highly specialized. In addition to these well-marked
brushes, the distal ends of the tibiae of the fore and middle legs bear
many stiff hairs, which function as pollen collectors, and the distal
tarsal joints of all legs bear similar structures.

Fig. 1. — Left foreleg of a worker bee. (Original.)

THE STRUCTURES CONCERNED.

9

The tibia and the planta of the hind leg of the worker bee are
greatly flattened. (See figs. 3, 4.) The outer surface of the tibia is
marked by an elongated depression, deepest at its distal end, and
bounded laterally by elevated margins. From the lateral boundaries
of this depression spring many long hairs, some of which arch over
the concave outer surface of the tibia and thus form a kind of recep-
tacle or basket to which the name corbicula or pollen-basket is given.
The lower or distal end of the tibia articulates at its anterior edge with
the planta. The remaining portion of this end of the tibia is flat-
tened and slightly concave, its

—Coxa

—^trochanter

-Femur

-Brush on Planta

surface sloping upward from
the inner to the outer surface
of the limb. Along the inner
edge of this surface runs a row
of short, stiff, backwardly di-
rected spines, from 15 to 21 in
number, which form the pec-
ten or comb of the tibia. The
lateral edge of this area forms
the lower boundary of the
corbicular depression and is
marked by a row of very fine
hairs which branch at their
free ends. Immediately above
these hairs, springing from the
floor of the corbicula, are found
7 or 8 minute spines, and above
them one long hair which
reaches out over the lower edge
of the basket.

The broad, flat planta (meta-
tarsus or proximal tarsal seg-
ment of the hind leg) is marked
on its inner surface by several
rows of stiff, distally directed
spines which form the pollen
combs. About 12 of these transverse rows may be distinguished,
although some of them are not complete. The most distal row, which
projects beyond the edge of the planta, is composed of very strong,
stiff spines which function in the removal of the wax scales (Casteel,
1912) . The upper or proximal end of the planta is flattened and pro-
jects in a posterior direction to form the auricle. The surface of the
auricle is marked with short, blunt spines, pyramidal in form, and a
fringe of fine hairs with branching ends extends along its lateral edge.
This surface slopes upward and outward.
61799°— Bull. 121—12 2

Fig. 2.

-Left middle leg of a worker bee.
( Original. )

10

BEHAVIOE OF HONEY BEE IN POLLEN COLLECTING.

--Femur

THE POLLEN SUPPLY.

When bees collect pollen from flowers they may be engaged in this
occupation alone or may combine it with nectar gathering. From
some flowers the bees take only nectar, from others only pollen; a

third class of flowers furnishes
an available supply of both of
these substances. But even
where both pollen and nectar
are obtainable a bee may
gather nectar and disregard
the pollen. This is well illus-
trated by the case of white
clover. If bees are watched
while working upon clover
flowers, the observer will soon
perceive some which bear pol-
len masses upon their hind
legs, while others will continue
to visit flower after flower,
dipping into the blossoms and
securing a plentiful supply of
nectar, yet entirely neglecting
the pollen.

The supply of pollen which
is available for the bees varies
greatly among different flow-
ers. Some furnish an abun-
dant amount and present it to
the bee in such a AYay that
little difficulty is experienced
in quickly securing an ample
load, while others furnish but
little. When flowers are small
and when the bee approaches
them from above, little, if any,
pollen is scattered over the
bee's body, all that it acquires
being first collected upon the
mouth and neighboring parts.
Very different conditions are
met with when bees visit such
plants as corn and ragweed. The flowers of these plants are pendent
and possess an abundant supply of pollen, which falls in showers over
the bodies of the bees as thev crawl beneath the blossoms. The

Ptanfa

Fig

-Outer surface of the left hind lej
worker bee. (Original.)

of a

GENERAL STATEMENT OF PROCESS.

11

-Femur

supply of pollen which lodges upon the body of the bee will thus
differ considerably in amount, depending upon the type of flower
from which the bee is collecting, and the same is true regarding the
location upon the body of a bee of pollen grains which are available
for storage in the baskets.
Moreover, the movements
concerned in the collection
of the pollen from the va-
rious body parts of the
bee upon which it lodges
will differ somewhat in
the two cases, since a
widely scattered supply
requires for its collection
additional movements,
somewhat similar in na-
ture to those which the
bee employs in cleaning
the hairs which cover its
body.

-Jlnleripr
edge

Posterior
edge-

"Stem*

GENERAL STATEMENT
OF THE POLLEN-COL-
LECTING PROCESS.

A very complete knowl-
edge of the pollen-gather-
ing behavior of the worker
honey bee may be obtained
by a study of the actions
of bees which are work-
ing upon a plant which
yields pollen in abun-
dance. Sweet corn is an
ideal plant for this pur-
pose, and it will be used
as a basis for the descrip-
tion which follows.

In attempting to out-
line the method by which
pollen is manipulated the
writer wishes it to be understood that he is recounting that which
he has seen and that the description is not necessarily complete,
although he is of the opinion that it is very nearly so. The move-
ments of the legs and of the mouthparts are so rapid and so many

Fig.

-Inner surface of the left hind leg
worker bee. (Original.)

of a

12 BEHAVIOR OF HONEY BEE IN POLLEN COLLECTING.

members are in action at once that it is impossible for the eye to
follow all at the same time. However, long-continued observation,
assisted by the study of instantaneous photographs, gives confidence
that the statements recorded are accurate, although some movements
may have escaped notice.

To obtain pollen from corn the bee must find a tassel in the right
stage of ripeness, with flowers open and stamens hanging from them.
The bee alights upon a spike and crawls along it. clinging to the
pendent anthers. It crawls over the anthers, going from one flower
to another along the spike, being all the while busily engaged in the
task of obtaining pollen. This reaches its body in several ways.

As the bee moves over the anthers it uses its mandibles and tongue,
biting the anthers and licking them and securing a considerable
amount of pollen upon these parts. This pollen becomes moist and
sticky, since it is mingled with fluid from the mouth. A considerable
amount of pollen is dislodged from the anthers as the bee moves over
them. All of the legs receive a supply of this free pollen and much
adheres to the hairs which cover the body, more particularly to those
upon the ventral surface. This free pollen is dry and powdery and
is very different in appearance from the moist pollen masses with
which the bee returns to the hive. Before the return journey this
pollen must be transferred to the baskets and securely packed in them.

After the bee has traversed a few flowers along the spike and has
become well supplied with free pollen it begins to collect it from its
body, head, and forward appendages and to transfer it to the pos-
terior pair of legs. This may be accomplished while the bee is
resting upon the flower or while it is hovering in the air before
seeking additional pollen. It is probably more thoroughly and rap-
idly accomplished while the bee is in the air, since all of the legs are
then free to function in the gathering process.

If the collecting bee is seized with forceps and examined after it
has crawled over the stamens of a few flowers of the corn, its legs
and the ventral surface of its body are found to be thickly powdered
over with pollen. If the bee hovers in the air for a few moments
and is then examined very little pollen is found upon the body or
upon the legs, except the masses within the pollen baskets. While in
the air it has accomplished the work of collecting some of the scat-
tered grains and of storing them in the baskets, while others have
been brushed from the body.

In attempting to describe the movements by which this result is
accomplished it will be best first to sketch briefly the roles of the
three pairs of legs. They are as follows :

(a) The first pair of legs remove scattered pollen from the head
and the region of the neck, and the pollen that lias been moistened
by fluid substances from the mouth.

ACTION OF FOEELEGS AND MOUTHPARTS. 13

(b) The second pair of legs remove scattered pollen from the
thorax, more particularly from the ventral region, and they re-
ceived the pollen that has been collected by the first pair of legs.

(c) The third pair of legs collect a little of the scattered pollen
from the abdomen and they receive pollen that has been collected
by the second pair. Nearly all of this pollen is collected by the
pollen combs of the hind legs, and is transferred from the combs to
the pollen baskets or corbiculse in a manner to be described later.

It will thus be seen that the manipulation of pollen is a succes-
sive process, and that most of the pollen at least passes backward
from the point where it happens to touch the bee until it finally
reaches the corbicula? or is accidentally dislodged and falls from the
rapidly moving limbs.

ACTION OF THE FORELEGS AND MOUTHPARTS.

Although the pollen of some plants appears to be somewhat sticky,
it may be stated that as a general rule pollen can not be successfully
manipulated and packed in the baskets without the addition of some
fluid substance, preferably a fluid which will cause the grains to
cohere. This fluid, the nature of which will be considered later,
comes from the mouth of the bee, and is added to the pollen which
is collected by the mouthparts and to that which is brought into con-
tact with the protruding tongue and maxilla?, and, as will appear,
this fluid also becomes more generally distributed upon the legs and
upon the ventral surface of the collecting bee.

When a bee is collecting from the flowers of corn the mandibles are
actively engaged in seizing, biting, and scraping the anthers as the
bee crawls over the pendent stamens. Usually, but not always, the
tongue is protruded and wipes over the stamens, collecting pollen
and moistening the grains thus secured. Some of the pollen may
possibly be taken into the mouth. - All of the pollen which comes in
contact with the mouthparts is thoroughly moistened, receiving more
fluid than is necessary for rendering the grains cohesive. This
exceedingly wet pollen is removed from the mouthparts by the fore-
legs (fig. 5), and probably the middle legs also secure a little of it
directly, since they sometimes brush over the lower surface of the
face and the mouth. In addition to removing the very moist pollen
from the mouth the forelegs also execute cleansing movements over
the sides of the head and neck and the anterior region of the thorax,
thereby collecting upon their brashes a considerable amount of pollen
which has fallen directly upon these regions, and this is added to the
pollen moistened from the mouth, thereby becoming moist by contact.
The brushes of the forelegs also come in contact with the anterior
breast region, and the hairs which cover this area become moist wTith
the sticky exudation which the forelegs have acquired in the process
of wiping pollen from the tongue, maxillae, and mandibles.

14

BEHAVIOE OF HONEY BEE IN POLLEN COLLECTING.

ACTION OF THE MIDDLE LEGS.

The middle legs are used to collect the pollen gathered by the
forelegs and mouthparts, to remove free pollen from the thoracic
region, and to transport their load of pollen to the hind legs, placing
most of it upon the pollen combs of these legs, although a slight
amount is directly added to the pollen masses in the corbiculse. Most
of the pollen of the middle legs is gathered upon the conspicuous
brushes of the first tarsal segments or plantse of these legs.

In taking pollen from a foreleg the middle leg of the same side is ex-
tended in a forward direction and is either grasped by the flexed fore-
leg or rubbed over the foreleg as it is bent downward and backward.
In the former movement the foreleg flexes sharply upon itself until

Pig. 5. — A flying bee, showing the manner in which the forelegs and middle legs manipu-
late pollen. The forelegs are removing wet pollen from the mouthparts and face. The
middle leg of the right side is transferring the pollen upon its brush to the pollen
combs of the left hind planta. A small amount of pollen has already been placed in
the baskets. (Original.)

the tarsal brush and coxa nearly meet. The collecting brush of the
middle leg is now thrust in between the tarsus and coxa of the fore-
leg and wipes off some of the pollen from the foreleg brush. The
middle leg brush is then raised and combs down over the flexed fore-
leg, thus removing additional pollen from the outer surface of this
leg. The middle leg also at times reaches far forward, stroking down
over the foreleg before it is entirely flexed and apparently combing
over with its tarsal brush the face and mouthparts themselves.
When the middle leg reaches forward to execute any of the above
movements the direction of the stroke is outward, forward, and then
back toward the body, the action ending with the brush of the leg in
contact with the long hairs of the breast and with those which spring

ACTION OF MIDDLE LEGS.

15

from the proximal segments of the forelegs (coxa, trochanter,
femur). As a result of the oft-repeated contact of the brushes of
the middle and forelegs with the breast, the long, branched hairs
which cover this region become quite moist and sticky, since the
brushes of these two pair of legs are wet and the pollen which they
bear possesses a superabundance of the moistening fluid. Any dry
pollen which passes over this region and touches these hairs receives
moisture by contact with them. This is particularly true of the free
dry pollen which the middle pair of legs collect by combing over the
sides of the thorax.

The pollen upon the middle legs is transferred to the hind legs in
at least two ways. By far the larger amount is deposited upon the
pollen combs which lie on the inner surfaces of the plantse of the

Fig. 6. — A bee upon the wing, showing the position of the middle legs when they touch
and pat down the pollen masses. A very slight amount of pollen reaches the corbiculre
through this movement. (Original.)

hind legs. To accomplish this a middle leg is placed between the
plantse of the two hind legs, which are brought together so as to grasp
the brush of the middle leg, pressing it closely between them, but
allowing it to be drawn toward the body between the pollen combs
of the two hind legs. (See fig. 5.) This action results in the trans-
ference of the pollen from the middle-leg brush to the pollen combs
of the hind leg of the opposite side, since the combs of that leg scrape
over the pollen-laden brush of the middle leg. This action may take
place while the bee is on the wing or before it leaves the flower.

The middle legs place a relatively small amount of pollen directly
upon the pollen masses in the corbiculse. This is accomplished when
the brushes of the middle legs are used to pat down the pollen masses
and to render them more compact. (See fig. 6.) The legs are used

16 BEHAVI0K OF HONEY BEE IX POLLEN COLLECTING.

for this purpose quite often during the process of loading the baskets,
and a small amount of pollen is incidentally added to the masses
when the brushes come into contact with them. A misinterpretation
of this action has led some observers into the erroneous belief that
all or nearly all of the corbicular pollen is scraped from the middle-
leg brushes by the hairs which fringe the sides of the baskets. The
middle legs do not scrape across the baskets, but .merely pat down-
ward upon the pollen which is there accumulating.

It is also possible that, in transferring pollen from the middle leg
of one side to the planta of the opposite hind leg, the middle-leg
brush may touch and rub over the pecten of the hind leg and thus
directly place some of its pollen behind the pecten spines. Such a
result is, however, very doubtful.

ACTION OF THE HIND LEGS.

The middle legs contribute the major portion of the pollen which
reaches the hind legs, and all of it in cases where all of the pollen
first reaches the bee in the region of the mouth. However, when
much pollen falls upon the body of the bee the hind legs collect a
little of it directly, for it falls upon their brushes and is collected
upon them when these legs execute cleansing movements to remove
it from the ventral surface and sides of the abdomen. All of the
pollen which reaches the corbicula?, with the exception of the small
amount placed there by the middle legs when they pat down the^
pollen masses, passes first to the pollen combs of the planta?.

"When in the act of loading pollen from the plantar brushes to the
corbicula? the two hind legs hang beneath the abdomen with the tibio-
femoral joints well drawn up toward the body. (See fig. 7.) The
two planta? lie close together with their inner surfaces nearly parallel
to each other, but not quite, since they diverge slightly at their distal
ends. The pollen combs of one leg are in contact with the pecten
comb of the opposite leg. If pollen is to be transferred from the
right planta to the left basket, the right planta is drawn upward in
such a manner that the pollen combs of the right leg scrape over
the pecten spines of the left. By this action some of the pollen is
removed from the right plantar combs and is caught upon the outer
surfaces of the pecten spines of the left leg.

This pollen now lies against the pecten and upon the flattened
distal end of the left tibia. At this moment the planta of the left
leg is flexed slightly, thus elevating the auricle and bringing the auri-
cular surface into contact with the pollen which the pecten has just
received. By this action the pollen is squeezed between the end of the
tibia and the surface of the auricle and is forced upward against the
distal end of the tibia and on outward into contact with the pollen
mass accumulating in the corbicula. As this act, by which the left

ACTION OF HIND LEGS.

17

basket receives a small contribution of pollen, is being completed, the
right leg is lowered and the pecten of this leg is brought into contact
with the pollen combs of the left planta, over which they scrape as
the left leg is raised, thus depositing pollen upon the lateral surfaces
of the pecten spines of the right leg. (See fig. 7.)

Eight and left baskets thus receive alternately successive contribu-
tions of pollen from the planta of the opposite leg. These loading
movements are executed with great rapidity, the legs rising and fall-
ing with a pump-like motion. A very small amount of pollen is
loaded at each stroke and many strokes are required to load the
baskets completely.

If one attempts to obtain, from the literature of apiculture and
zoology, a knowledge of the method by which the pollen baskets

Fig. 7. — A bee upon the wing, showing the manner in which the hind legs are held during
the basket-loading process. Pollen is being scraped by the pecten spines of the right
leg from the pollen combs of the left hind planta. (Original.)

themselves are loaded, he is immediately confused by the diversity of
the .accounts available. The average textbook of zoology follows
closely Cheshire's (1886) description in which he says that " the legs
are crossed, and the metatarsus naturally scrapes its comb face on the
upper edge of the opposite tibia in the direction from the base of the
combs toward their tips. These upper hairs * * * are nearly
straight, and pass between the comb teeth. The pollen, as removed,
is caught by the bent-over hairs, and secured. Each scrape adds to
the mass, until the face of the joint is more than covered, and the
hairs just embrace the pellet." Franz (1906) states that (translated)
" the final loading of the baskets is accomplished by the crossing over
of the hind-tarsal segments, which rub and press upon each other."
Many other observers and textbook writers evidently believed that
the hind legs were crossed in the loading process.
61799°— Bull. 121—12 3

18 BEHAVIOR OF HONEY BEE IK" POLLEN COLLECTING.

On the other hand, it is believed by some that the middle legs are
directly instrumental in filling the baskets. This method is indicated
in the following quotation from Fleischmann and Zander (1910)
(translated) :

The second pair of legs transfer the pollen to the hind legs, where it is
heaped up in the pollen masses. The tibia of each hind leg is depressed on its
outer side, and upon the edges of this depression stand two rows of stiff hairs
which are bent over the groove. The brushes of the middle pair of legs rub
over these hairs, liberating the pollen, which drops into the baskets.

A suggestion of the true method is given by Hommell (1906),
though his statements are somewhat indefinite. After describing
the method by which pollen is collected, moistened, and passed to
the middle legs he states that (translated) "the middle legs place
their loads upon the pollen combs of the hind legs. There the sticky
pollen is kneaded and is pushed across the pincher (a traverse la
pince), is broken up into little masses and accumulates within the
corbicula. In accomplishing this, the legs cross and it is the tarsus
of the right leg which pushes the pollen across the pincher of the
left, and reciprocally. The middle legs never function directly in
loading the baskets, though from time to time their sensitive ex-
tremities touch the accumulated mass, for the sake of giving assur-
ance of its position and size."

The recent valuable papers of Sladen (1911, 1912, a, 6, c* cL and e),
who was the first to present a true explanation of the function of
the abdominal scent gland of the bee, give accounts of the process
by which the pollen baskets are charged, which are in close accord
with the writer's ideas on this subject. It is a pleasure to be able to
confirm most of Sladen's observations and conclusions, and weight is
added to the probable correctness of the two descriptions and in-
terpretations of this process by the fact that the writer's studies and
the conclusion based upon them were made prior to the appearance
of Sladen's papers and quite independent of them. His description
of the basket-loading process itself is so similar to the writer's own
that a complete quotation from him is unnecessary. A few differences
of opinion will, however, be noted while discussing some of the move-
ments which the process involves. As will later be noted, our ideas
regarding the question of pollen moistening, collecting, and transfer-
ence are somewhat different.

ADDITIONAL DETAILS OF THE BASKET-LOADING PROCESS.

The point at which pollen enters the basket can best be determined
by examining the corbicula? of a bee shortly after it has reached a
flower and before much pollen has been collected. Within each
pollen basket of such a bee is found a small mass of pollen, which lies

ADDITIONAL DETAILS OF BASKET-LOADING PROCESS.

19

along the lower or distal margin of the basket. (See fig 8, a.) It is
in this position because it has been scraped from the planta of the
opposite leg by the pecten comb and has been pushed upward past
the entrance of the basket by the continued addition of more from
below, propelled by the successive strokes of the auricle. Closer

Fig. 8. — Camera drawings of the left hind legs of worker bees to show the manner in
which pollen enters the basket, a, Shows a leg taken from a bee which is just begin-
ning to collect. It had crawled over a few flowers and had flown in the air about five
seconds at the time of capture. The pollen mass lies at the entrance of the basket,
covering over the fine hairs which lie along this margin and the seven or eight short
stiff spines which spring from the floor of the corbicula immediately above its lower
edge. As yet the pollen has not come in contact with the one long hair which rises
from the floor and arches over the entrance. The plauta is extended, thus lowering
the auricle ; b, represents a sligbtly later stage, showing the increase of pollen. The
planta is flexed, raising the auricle. The hairs which extend outward and upward from
the lateral edge of the auricle press upon the lower and outer surface of the small
pollen mass, retaining it and guiding it upward into the basket ; v, d, represent slightly
later stages in the successive processes by which additional pollen enters the basket.
(Original.)

examination of the region between the pecten and the floor of the
basket itself shows more pollen, which is on its way to join that
already squeezed into the basket.

If the collecting bee is watched for a few moments the increase will
readily be noted and the fact will be established that the accumulat-
ing mass is gradually working upward or proximally from the lower

20 BEHAVIOK OF HONEY BEE IN POLLEN COLLECTING.

or distal edge of the corbicula and is slowly covering the floor of this
receptacle. (See fig. 8, 5, <?, and d.) In many instances the suc-
cessive contributions remain for a time fairly separate, the whole
mass being marked by furrows transverse to the long axis of the tibia.

Sladen (1912, b) notes the interesting fact that in those rather
exceptional cases when a bee gathers pollen from more than one
species of flowers the resulting mass within the corbicula will show
a stratification parallel to the distal end, a condition which could
result only from the method of loading here indicated.

As the pollen within the basket increases in amount it bulges out-
ward, and projects downward below the lower edge of the basket.
It is held in position by the long hairs which fringe the lateral sides
of the basket, and its shape is largely determined by the form of
these hairs and the direction in which they extend. When the basket
is fully loaded the mass of pollen extends laterally on both sides of
the tibia, but projects much farther on the posterior side, for on this
side the bounding row of hairs extends outward, while on the anterior
edge the hairs are more curved, folding upward and over the basket.
As the mass increases in thickness by additions from below it is held
in position by these long hairs which edge the basket. They are
pushed outward and many of them become partly embedded in the
pollen as it is pushed up from below. When the pollen grains are
small and the whole mass is well moistened the marks made by some
of the hairs will be seen on the sides of the load. (See fig. 9, a.)
These scratches are also transverse in direction and they show that
the mass has been increased by additions of pollen pushed up from
below.

Even a superficial examination of a heavily laden basket shows
the fallacy of the supposition that the long lateral fringing hairs are
used to comb out the pollen from the brushes of either the hind or
middle legs by the crossing of these legs over the lateral edges of the
baskets. They are far from sufficiently stiff to serve this purpose,
and their position with relation to the completed load shows con-
clusively that they could not be used in the final stages of the loading-
process, for the pollen mass has completely covered many of them
and its outer surface extends far beyond their ends. They serve
merely to hold the pollen in place and to allow the load to project
beyond the margins of the tibia.

The auricle plays a very essential part in the process of loading
the basket. This structure comprises the whole of the flattened
proximal surface of the planta, except the joint of articulation itself,
and it extends outward in a posterior direction a little beyond the
remaining plantar edge. The surface of the auricle is covered over
with many blunt, short spines and its lateral margin is bounded by
a row of short rather pliable hairs, branched at their ends. When

ADDITIONAL DETAILS OF BASKET-LOADING PKOCESS. 21

the planta is flexed the auricle is raised and its surface approaches
the distal end of the tibia, its inner edge slipping up along the pecten
spines and its outer hairy edge projecting into the opening which
leads to the pollen basket. (See fig. 8, h.) With each upward stroke
of the auricle small masses of pollen which have been scraped from the

J plantar combs by the pecten are caught and compressed between the
spiny surface of the auricle and the surface of the tibia above it.

j The pressure thus exerted forces the pasty pollen outward and up-
ward, since it can not escape past the base of the pecten, and directs
it into the entrance to the corbicula. The outward and upward slant

J of the auricular surface and the projecting hairs with which the outer

edge of the auricle is supplied also aid in directing the pollen toward

1 the basket. Sladen (1911) states that in this movement the weak

j wing of the auricle is forced backward, and thus allows the escape of

t pollen toward the basket entrance, but this appears both doubtful and
'unnecessary, since the angle of inclination of the auricular surface
j gives the pollen a natural outlet in the proper direction.

If the corbicula already contains a considerable amount of pollen
the contributions which are added to it at each stroke of the auricle
come in contact with that already deposited and form a part of this
mass, which increases in amount by continued additions from below.
If, however, the corbicula is empty and the process of loading is just
beginning, the first small bits of pollen which enter the basket must
be retained upon the floor of the chamber until a sufficient amount
has accumulated to allow the long overcurving hairs to offer it effec-
tive support. The sticky consistency of the pollen renders it likely
to retain contact with the basket, and certain structures near the
entrance give additional support. Several small sharp spines, seven
or eight in number, spring from the floor of the basket immediately
within the entrance, and the entire lower edge of the corbicula is

I fringed with veiy small hairs which are branched at their ends.
(See fig. 3.) One large hair also springs from the floor of the basket,
somewhat back from the entrance, which may aid in holding the

i pollen, but it can not function in this manner until a considerable
amount has been collected.

As the pollen mass increases in size and hangs downward and back-

i ward over the pecten and auricle it shows upon its inner and lower
surface a deep groove which runs outward from the entrance to the
basket. (See fig. 9, b.) This groove results from the continued im-
pact of the outer end of the auricle upon the pollen mass. At each
upward stroke of the auricle its outer point comes in contact with
the stored pollen as soon as the mass begins to bulge backward from
the basket.

Although the process is a rather delicate one, it is entirely pos-
sible so to manipulate the hind legs of a recently killed bee that the

22

BEHAVIOR OF HOXEY BEE IX POLLEN COLLECTING.

-&

corbiculse of the two legs receive loads of pollen in a manner similar
to that above described. To accomplish this successfully the operator
must keep the combs of the plantse well supplied with moistened
pollen. If the foot of first one leg and then the other is grasped
with forceps and so guided that the pollen combs of one leg rasp over
the pectert spines of the other, the pollen from the combs will be
transferred to the corbicula?. To continue the loading process in a

proper manner, it is also nec-
essary to flex the plant a of
each leg just after the pollen
combs of the opposite leg
have deposited pollen behind
the pecten. By this action
the auricle is raised, com-
pressing the pollen which
the pecten has secured, and
forcing some upward into
the corbicula. Bees' legs
which have been loaded in
this artificial manner show
pollen masses in their cor-
biculse which are entirely
similar in appearance to
those formed by the labors
of the living bee. More-
over, by the above method
of manipulation the pollen
appears first at the bottom
of the basket, along its lower
margin, gradually extends
upward along the floor of
the chamber, comes in con-
tact with the overhanging
hairs, and is shaped by them
in a natural manner. All
attempts to load the baskets
bv other movements, such as

Fig. 9. — Inner surface of the right hind leg of a
worker bee which bears a complete load of
pollen, a, Scratches in the pollen mass caused
by the pressure of the long projecting hairs
of the basket upon the pollen mass as it has
been pushed up from below ; 1), groove in the
pollen mass made by the strokes of the auricle
as the mass projects outward and backward
from the basket. (Original.)

crossing the hind legs and

scraping the plantar combs over the lateral edges of the baskets,
give results which are entirelv different from those achieved by the

living bee.

POLLEN MOISTENING.

Many descriptions have been written by others of the method by
which pollen is gathered and moistened. Some of these are indefi-
nite, some are incorrect, while others are. in part, at least, similar

POLLEN MOISTENING. 23

to my own interpretation of this process. A few citations will here
be given :

The bee first strokes the head and the proboscis with the brushes of the
forelegs and moistens these brushes with a little honey from the proboscis, so
that with later strokes all of the pollen from the head is collected upon these
brushes. Then the middle-leg brushes remove this honey-moistened pollen from
the forelegs and they also collect pollen from the breast and the sides of the
thorax. — [Translation from Alefeld, 1861.]

In his account of the basket-loading process Alefeld assigns to
the middle-leg brushes the function of assembling all of the pollen,
even that from the plantar combs, and of placing it on the corbiculse,
this latter act being accomplished by combing over the hairy edge of
each basket with the middle-leg brush of the same side.

It appears probable that the bee removes the pollen from the head, breast,
and abdomen by means of the hairy brushes which are located upon the medial
sides of the tarsal segments of all of the legs, being most pronounced upon the
hind legs. The pollen is thus brought together and is carried forward to the
mouth, where it is moistened with saliva and a little honey. — [Translation from
Franz, 1906.]

Franz then says that this moistened pollen is passed backward and
loaded.

Since the pollen of many plants is sticky and moist it adheres to the surface
of the basket. Dry pollen is moistened by saliva, so that it also sticks. —
[Translation from Fleischmann and Zander, 1910.]

Pollen is taken from flowers principally by means of the tongue, but at times,
also, by the mandibles, by the forelegs, and middle legs. The brushes of the
hind legs also load themselves, collecting from the hairs of the body. The pollen
dust thus gathered is always transmitted to the mouth, where it is mixed with
saliva. — [Translation from Hommell, 1906.]

Sladen considers the question of how pollen is moistened by the
honey bee, humblebee ( bumblebee) , and some other bees, but does not
appear to reach definite conclusions. In one of his papers (1912, c)
he states that the pollen of some plants may be found in the mouth
cavity and in the region of the mouth, but he reaches the conclusion
that this pollen is comparatively " dry," using the word in a " rela-
tive sense." He asserts that " nowhere but on the corbicula and
hind metatarsal brushes did I find the sticky pollen, except some-
times on the tips of the long, branched hairs on the back (upper)
edges of the tibia? and femora of the middle legs, and then only
in heavily laden bees, where it is reasonable to suppose it had
collected accidentally as the result of contact with the hind metatarsal
brushes."

These and other considerations lead Sladen to think that, in the
case of the bumblebee at least, the pollen " may be moistened on the
hind metatarsus with the tongue." He states that the tongue of
the bumblebee is of sufficient length to reach the hind metatarsus

24 BEHAVIOR OF HOSTEY BEE IN POLEEX COLLECTING.

(planta) and that it might rub over the brushes of the metatarsi
or be caught between them when they are approximated and thus
moisten the two brushes simultaneously. However, he has never
seen the tongue of the collecting honey bee brought near to the hind
legs, and it appears probable to him that it can not easily reach them.
" Possibly the middle or front legs are used as agents for conveying
the honey" (in the case of the honey bee). "In the humblebee the
tongue is longer, and it could more easily moisten the hind legs in
the way suggested."

In an earlier paper Sladen (1912, a) gives the following as his
opinion of the " way in which pollen dust is moistened with nectar,"
although he states that this is one of the points " which still remains
obscure " :

The only satisfactory manner in which, it seems to me, this can be done is
for the tongue to lick the tarsi or metatarsi of the forelegs, which are covered
with stiff bristles, well suited for holding the nectar, the nectar being then
transferred to the metatarsal brushes on the middle legs, and from these, again,
to the metatarsal brushes on the hind legs. The latter being thus rendered
sticky, the pollen dust would cling to them. The different pairs of legs were
certainly brought together occasionally, but not after every scrape of the
hind metatarsi, and their movements were so quick that it was impossible
to see what was done. Still, several polleu-collectiug bees that I killed had the
tarsi and metatarsi of the forelegs and the metatarsal brushes of the middle
and hind legs moistened with nectar, and I think it probable that the moisten-
ing process, as outlined, is performed, as a rule, during the flight from flower
to flower.

Sladen (1912, <~) also considers the possibility that the fluid which
moistens the pollen might be secreted through the comb at the end
of the tibia, through the tibio-tarsal joint, or from the surface of the
auricle, but finds no evidence of glandular openings in these regions.
A suggestion of a similar nature, apparently unknown to Sladen,
was made by Wolff (1873), who describes "sweat-glands" which,
he claims, are located within the hind tibia and the planta, and
which pour a secretion upon the surface of the corbicula and upon
the upper end of the planta through many minute openings located
at the bases of hairs, particularly those which arise from the lateral
margins of the corbicula. Wolff is convinced that the fluid thus
secreted is the essential cohesive material by which the grains of
pollen are bound together to form the solid mass which fills each
fully loaded basket. He noticed that the mouthparts are used to
collect pollen, and that some of it is moistened with " honey " or
"nectar," but he does not consider that the fluid thus supplied is
sufficient to explain adequately the facility with which the collecting
bee brings together the scattered grains of pollen and packs them
away securely in the baskets. Wolff's description of the basket-load-
ing process itself is strikingly similar to that advocated later bj
Cheshire.

POLLEN MOISTENING. 25

The writer is not prepared to deny the possibility that the surface
of the chitin of the hind legs of worker bees may be moistened by
the secretion of glands which lie beneath it, but he is convinced that
any fluid thus secreted bears little or no relation to the cohesion of
the pollen grains within the baskets. Sections and dissected prepa-
rations of the hind legs of worker bees show certain large cells which
lie within the cavity of the leg and which may function as secreting
gland cells; but similar structures occur in even greater numbers
within the hind legs of the drone and they are found within the hind
legs of the queen.

As has been noted, the extreme moisture of the plantar combs and
of the tibio-tarsal articulation of the hind leg is readily understood
when one recalls the manner in which moist pollen is compressed
between the auricle and the tibial surface above it.

From the account already given it is evident that, in the opinion
of the writer, the mouth is the source from which the pollen-moisten-
ing fluid is obtained. It is extremely difficult to determine with
absolute accuracy the essential steps involved in the process of adding
moisture to the pollen. In an endeavor to solve this problem the
observer must of necessity consider a number of factors, among which
may be noted (1) the location upon the body of the collecting bee
of " moist " and of comparatively " dry " pollen, (2) the movements
concerned in the pollen-gathering and pollen-transferring processes,
(3) the relative moisture of those parts which handle pollen, (4) the
chemical differences between the natural pollen of the flower and
that of the corbiculse and of the cells of the hive, and (5) the observer
must endeavor to distinguish between essential phenomena and those
it which are merely incidental or accidental.

In the first place it should be noted that the relative dampness of
pollen within the corbiculse depends very largely upon the character
of the flower from which the pollen grains are gathered. When
little pollen is obtained it is much more thoroughly moistened, and
| this is particularly true in cases when the pollen is all, or nearly all,
I collected in the region of the mouth, the forelegs, and head. When
I a bee takes pollen from white or sweet clover practically all of it
f first touches the bee in these regions. It immediately becomes moist,
{ and in this condition is passed backward until it rests within the
baskets. There is here no question of "dry" and "wet" pollen,
or of collecting movements to secure dry pollen from other regions
of the body, or of the ultimate method by which such free, dry pol-
len becomes moist.

The sticky fluid which causes pollen grains to cohere is found upon
all of the legs, in the region of their brushes, although the pollen
combs and auricles of the hind legs are likely to show it in greatest
abundance, since nearly all of the pollen within each basket has

r

26 BEHAVIOE OF HONEY BEE IN POLLEN COLLECTING.

passed over the auricle, has been pressed upward and squeezed be-
tween the auricle and the end of the tibia and the pollen mass above,
and by this compression has lost some of its fluid, which runs down
over the auricle and onto the combs of the planta. It is not necessary
to invoke any special method by which these areas receive their
moisture. The compressing action of the auricle squeezing heavily
moistened pollen upward into the basket is entirely sufficient to
account for the abundance of sticky fluid found in the neighborhood
of each hind tibio-tarsal joint. As has been noted, the brushes of
the forelegs acquire moisture directly by stroking over the proboscis
and by handling extremely moist pollen taken from the mouthparts.
The middle-leg brushes become moist by contact with the foreleg and
hind-leg brushes, probably also by touching the mouthparts them-
selves, and by passing moist pollen backward. The hairy surface of
the breast is moistened by contact with the fore and mid leg brushes
and with the moist pollen which they bear.

The problem of the method of pollen moistening is somewhat more
complicated in the case of flowers which furnish an excessive supply.
Under such conditions the entire ventral surface of the collecting bee
becomes liberally sprinkled with pollen grains which either will be
removed and dropped or will be combed from the bristles and branch-
ing hairs, kneaded into masses, transferred, and loaded. The ques-
tion naturally arises whether the movements here are the same as
when the plant yields but a small amount of pollen which is collected
by the mouthparts and anterior legs. In the opinion of the writer
they are essentially the same, except for the addition of cleansing
movements, executed chiefly by the middle and hind legs for the col-
lection of pollen which has fallen upon the thorax, upon the abdomen,
and upon the legs themselves. Indeed it is questionable as to just
how much of this plentiful supply of free pollen is really used in
forming the corbicular masses. Without doubt much of it falls from
the bee and is lost, and in cases where it is extremely abundant and
the grains are very small in size an appreciable amount still remains
entangled among the body-hairs when the bee returns to the hive.
Yet it is also evident that some of the dry pollen is mingled with the
moistened material which the mouthparts and forelegs acquire and
together with this is transferred to the baskets.

In all cases the pollen-gathering process starts with moist pollen
from the mouth region. This pollen is passed backward, and in its
passage it imparts additional moisture to those body regions which
it touches, the brushes of the fore and middle legs, the plantse of the
hind legs, and the hairs of the breast which are scraped over by the
fore and middle leg brushes. This moist pollen, in its passage back-
ward, may also pick up and add to itself grains of dry pollen with
which it accidentally comes in contact. Some of the free, dry pollen

POLLEN MOISTENING. 27

which falls upon the moist brushes or upon the wet hairs of the
thorax is also dampened. Some of the dry pollen which is cleaned
from the body by the action of all of the legs meets with the wet
brushes or with the little masses of wet pollen and itself becomes wet
by contact. Pollen grains which reach the corbiculse either dry or
but slightly moistened are soon rendered moist by contact with those
already deposited. Little pollen gets by the sticky surfaces of the
combs of the plants or past the auricles without becoming thoroughly
moist.

Sladen (1912, c) very aptly compares the mixture of dry pollen
with wet to the kneading of wet dough with dry flour and suggests
that the addition of dry pollen may be of considerable advantage,
since otherwise the brushes, particularly those of the hind legs,
would become sticky, " just as the board and rolling pin get sticky
in working up a ball of dough if one does not add flour." The addi-
tion of a considerable amount of dry pollen gives exactly this result,
for the corbiculse then rapidly become loaded with pollen mixed
with a minimum supply of moisture and the brushes remain much
dryer than would otherwise be the case. However, if too much dry
pollen is added the resulting loads which the bees carry back to the
hives are likely to be irregular, for the projecting edges of the masses
may crumble through lack of a sufficient amount of the cohesive
material by which the grains are bound together.

On the other hand, it does not appear at all necessary to mix much
dry pollen with the wet, nor do the brushes become sufficiently
" sticky " from the presence of an abundance of the moistening fluid
to endanger their normal functional activity. I have observed bees
bringing in pollen masses which were fairly liquid with moisture,
and the pollen combs also were covered with fluid, yet the baskets
were fully and symmetrically loaded.

Sladen's different interpretations of the pollen-moistening process
are rather confusing, and it is difficult to distinguish between what
he states as observed facts and what he puts forward as likely
hypotheses. He agrees with me in his observation that all of the
legs become moist in the region of their brushes and also in his sup-
position that this moisture is transferred to them from the mouth.
In this moistening process my observations show that the fluid con-
cerned is passed backward by the contact of the middle-leg brushes
with the wet foreleg brushes and that the middle-leg brushes in turn
convey moisture to the plantse as they rub upon them. I am also
convinced that the wet pollen grains furnish additional moisture to
the brushes as they pass backward, and this is particularly true in
the case of the extremely moist surfaces of the auricles and the pollen
combs of the planta, since here moisture is pressed from the pollen
upon these areas. The pollen upon the fore and middle leg brushes
is not always " dry " even in " a relative sense."

28

BEHAVIOR OF HONEY BEE IX POLLEN COLLECTING.

In describing pollen manipulation several writers state that dry
pollen is picked up by the brushes of the legs and is carried forward
to the mouth, there moistened (according to some, masticated), and
is then carried backward by the middle legs for loading. Obviously
such accounts do not apply to cases in which all of the pollen is col-
lected by mouthparts and forelegs. Do they apply in cases where
much pollen falls on the body and limbs? Without doubt a certain
amount of this free pollen is brought forward when the middle legs,
bearing some of it, sweep forward and downward over the forelegs,
mouthparts, and breast. However, it does not appear to the writer
that this dry pollen is carried to the mouth for the specific purpose of
moistening it, or that it is essential to its moistening that it be
brought in contact with the mouth. Some of it touches the moist
hairs on the forelegs and breast and is moistened by contact. All
that remains on the brushes of the middle legs secures moisture from
these brushes or from wet pollen which the brushes collect from the
mouthparts or forelegs. The supposed necessity of carrying forward
pollen to the mouth for moistening is a delusion. Some is acci-
dental^7 brought forward and into contact with the mouth and gets
wet, but the process is not essential.

If the pollen which bees transport to their hives has been moistened
with some fluid substance which causes the grains to cohere, this
addition should be indicated by differences in the results of an analy-
sis of pollen from a plant as compared with that found in the cor-
biculse of a bee which has been working on this plant. For the sake
of determining this difference and in an endeavor to ascertain, if
possible, the approximate nature of the added fluid, analyses were
made of three kinds of pollen, as follows: (1) Pollen collected by
hand from the corn plant itself; (2) pollen taken from the corbiculpe
of bees which had secured their supply from corn; (3) pollen stored
in the cells of the hive. In the first two cases pollen from the same
species of plant (corn) was used. The material from the cells of the
hive was composed largely of corn pollen, but contained an admixture
of some other pollens.

The writer is indebted to Dr. P. B. Dunbar, of the Bureau of
Chemistry, for the following analyses :

Pollen
direct
from
corn.

Corn pol-
len from
corbieula.

Stored
pollen
from
hive.

53.47

46.53
2.87
2.77
5.79

66.94
33. 06
11.07
3.06

14.29

79.66

20.34

17.90

2.25

Total reducing sugar after inversion

20.27

Dry basis:

£.37
5.18

16.54
4.57

22 47

Sucrose

2.82

10.55

21.11

STOKING POLLEN IN THE HIVE. 29

These analyses show conclusively that a very large amount of
sugar has been added to the pollen by the time it reaches the cor-
biculse. Calculated on a dry basis just about twice as much sugar is
present in the basket pollen as in that from the corn plant. Not only
is this so, but the additional fact is disclosed that over three times as
much reducing sugar is present in the corbicular pollen as sucrose.
This latter result indicates that honey (largely a reducing sugar)
rather than nectar (containing more sucrose) is the chief sugar in-
gredient of the corbicular pollen. The additional amount of sugar
(here again a reducing sugar) in the stored pollen- of the hive is
what might be expected, since it is supposed that the workers add
honey and possibly other ingredients to the pollen within the
storage cells.

The total solid percentages, corn 53.47, corbicula 66.94, stored
pollen 79.66, also show that the fluid substance which is added is one
highly charged with solids, a condition which honey amply fulfills.

In the descriptions which have been cited of the pollen-gathering
process in which the mouth is supposed to supply the requisite fluid
three substances are mentioned: Nectar, honey, and saliva. The
analyses herein given indicate that reducing sugar is mingled with
the pollen, and in the case of corn it is indicated that honey is used
in .greater abundance. Without doubt a certain amount of saliva
also finds its way to the pollen, but the proportion of this substance
has not been determined. This salivary fluid may have adhesive
qualities, but this is scarcely necessary, since honey alone is amply
sufficient for this purpose.

It appears probable that the fluid which a bee adds to the pollen
which it is collecting varies somewhat in amount, since the pollen of
different plants differs- considerably in moisture content and that of
the same plant will differ in this respect at different times. Pollen
collected in the early morning before the dew has left the plant is
much more moist than that found upon the same plant later in the
day, and the grains, if taken when moist, have a natural tendency to
become aggregated and form small masses. Moreover, this may ex-
plain the fact that bees make their pollen-collecting trips during the
morning hours, rather than in the afternoon, although some may be
seen upon the flowers throughout the whole day.

STORING POLLEN I2T THE HIVE.

When the bee has fully loaded its baskets and before it returns to
the hive it often spends a little time upon the plant from which it
has been collecting, occupied with the task of cleaning scattered
grains of pollen from its body and of patting down securely the loads
which it has obtained. Upon its return to the hive it hurries within
and seeks for a suitable place in which to deposit the pollen. Some

30 BEHAVIOE OF HONEY BEE IN POLLEN COLLECTING.

returning bees walk leisurely over the combs and loiter among their
sister workers, while others appear to be greatly agitated, shaking
their bodies and moving their wings as though highly excited.
Many pollen-bearing bees appear eager to receive food upon their
return to the hive, and they will solicit it from other workers or
take it from the honey-storage cells. The workers of the hive at *
times take a little of the fresh pollen from the baskets of the laden 1
bee, nibbling it off with their mandibles or rasping off grains with
their tongues.

If the combs, of a colony are examined, stored pollen will be found
in various parts of the hive. In the brood frames the greatest amount '
is located above and at the sides of the brood and between this and
the stored honey. Cells scattered through the brood from which
young bees have lately emerged may also contain pollen. In the
outer frames of the hive, where brood is less likely to be found, j
nearly all of the cells may be packed with pollen, or honey-storage
cells may be found interspersed with those filled with pollen. As a > -j
rule pollen is not stored in drone comb, although this occasionally k
happens. 1

As the pollen-bearing bee crawls over the combs it appears to be <
searching for a suitable cell in which to leave its load. It sticks
the head into cell after cell until finally one is located which meets
its requirements, although it is an open question as to why any one of
a group should be chosen rather than another. This selected cell
may already contain some pollen or it may be empty. If partly filled,
the pollen which it contains is likely to be from the same species of
plant as that which the bee carries, although different kinds of pollen
are often stored in the same cell.

In preparation for the act of unloading the bee grasps one edge y
of the cell with its forelegs and arches its abdomen so that the pos-
terior end of the abdomen rests upon the opposite side of the cell. The \
body is thus held firmly and is braced by these two supports with the «
head and anterior thoracic region projecting over one of the neigh- I
boring cells. The hind legs are thrust down into the cell and hang
freely within it, the pollen masses being held on a level with the outer ^
edge of the cell, or slightly above it. The middle leg of each side ,
is raised and its planta is brought into contact with the upper .
(proximal) end of the tibia of the same side and with the pollen mass, i
The middle leg now presses downward upon the pollen mass, work- i
ing in between it and the corbicular surface, so that the mass is
shoved outward and downward and falls into the cell. As the pollen
masses drop, the middle legs are raised and their claws find support
upon the edge of the cell. The hind legs now execute cleansing move-
ments to remove small bits of pollen which still cling to the corbicular

SXJMMAKY. 31

surfaces and hairs. After this is accomplished the bee usually leaves
the cell without paying further attention to the two pellets of pollen
although some collecting bees will stick the head into the cell, possi-
bly to assure themselves that the pollen is properly deposited. It has
been stated by some (Cheshire, for example) that the spur upon the
middle leg is used to help pry the pollen mass from the corbicula.
This structure is in close proximity with the mass while the middle
leg is pushing downward upon it, but its small size renders difficult
an exact estimate of its value in this connection. It is certainly true
that the entire planta of the middle leg is thrust beneath the upper
end of the pollen mass, but the spur may be used as an entering
wedge.

Pollen masses which have been dropped by the collecting bee may
remain for some time within the cell without further treatment, but
usually another worker attends to the packing of the pollen shortly
after it has been deposited. To accomplish this the worker enters the
cell head first, seizes the pollen pellets with its mandib]es, breaks
them up somewhat or flattens them out, probably mingles additional
fluid with the pollen, and tamps down the mass securely in the bot-
tom of the cell. As is shown by the analyses of corbicular pollen and
of stored pollen, certain substances are added to the pollen after the
collecting bee leaves it in the cell. Sugar is certainly added, and it is
generally supposed that secretions from some of the salivary glands
are mixed with the pollen after deposition. It appears probable that
the stored pollen or " beebread " is changed somewhat in chemical
composition through the action of the fluids which have been added
to it, either during the process of collection, at the time of packing,
or later.

SUMMARY.

Pollen may be collected by the worker bee upon its mouthparts,
upon the brushes of its legs, and upon the hairy surface of its body.
When the bee collects from small flowers, or when the supply is not
abundant, the mouthparts are chiefly instrumental in obtaining the
pollen.

The specialized leg brushes of the worker are used to assemble the
pollen, collecting it from the body parts to which it first adheres and
transporting it to the pollen baskets or corbiculse of the hind legs. In
this manipulation the forelegs gather pollen from the mouthparts and
head; the middle legs, from the forelegs and from the thorax; the
hind legs, from the middle legs and from the abdomen.

The pollen baskets are not loaded by the crossing over of one hind
leg upon the other or to any great extent by the crossing of the middle
legs over the corbiculse. The middle legs deposit their loads upon the

32 BEHAVIOR OF HONEY BEE IN POLLEN COLLECTING.

pollen combs of the hind plants, and the plantse, in turn, transfer the
pollen of one leg to the pecten comb of the other, the pecten of one
leg scraping downward over the pollen comb of the opposite leg.
(See fig. 7.) A little pollen is loaded directly from the middle legs
into the baskets when these legs are used to pat down the pollen
masses. (See fig. 6.)

Aside from the foregoing exception, all of the pollen which reaches
the baskets enters them from below, since it is first secured by the
pecten combs, and is then pushed upward by the impact of the
rising auricles, which squeeze it against the distal ends of the tibiae
and force it on into the baskets to meet that which has gone before.

The long hairs which form the lateral boundaries of the baskets
are not used to comb out pollen from the brushes of any of the legs.
They serve to retain the accumulating masses within the baskets and
to support the weight of the pollen, as it projects far beyond the
surfaces of the tibia?.

Pollen grains are moistened and rendered cohesive by the addition
to them of fluid substances which come from the mouth. Analyses
show that honey forms a large part of this moistening fluid, although
nectar and secretions from the salivary glands are probably present
also.

In the process of pollen manipulation this fluid substance becomes
well distributed over the brushes of all of the legs. The forelegs
acquire moisture by brushing over the mouthparts, and they transfer
this to the hairs of the breast and to the middle-leg brushes when
they come in contact with them. The middle-leg brushes transmit
their moisture to the pollen combs of the hind legs when they rub
upon them. All of these brushes also transport wet pollen which
has come from the mouthparts and thereby acquire additional mois-
ture. The auricles and the plantse of the hind legs become particu-
larly wet from this source, since fluid is squeezed from the wet pollen
when it is compressed between the auricles and the distal ends of the
tibiae. Dry pollen which falls upon the body hairs becomes moist
when brought into contact with the wet brushes or with wet pollen.

During the process of manipulation pollen passes backward from
its point of contact with the bee toward its resting place within the
baskets.

Pollen which the collecting bee carries to the hive is deposited by
this bee within one of the cells of the comb. As a rule, this pollen is
securely packed in the cell by some other worker, which flattens out
the rounded masses and adds more fluid to them.

BEHAVIOE OF HONEY BEE IN POLLEN COLLECTING. 33

BIBLIOGRAPHY.

Alefeld, Dr. — Vol. 5, Nos. 15 and 16, Eichstadt Bienen Zeitung. Summarized

in "Die Bienenzeitung in neuer, geschichteter und systematische geordneter

Ausgabe." Herausgegeben vom Schmid und Kleine : Erste Band,

Theoretischer Theile. 1861.

Casteel, D. B., 1912. — The manipulation of the wax scales of the honey bee,

Circular 161, Bureau of Entomology, U. S. Dept. Agriculture, pp. 15.
Cheshire, F. R., 1886. — Bees and bee-keeping; scientific and practical. Vol. I,

scientific ; II, practical. London.
Fleischmann und Zander, 1910. — Beitrage zur Naturgeschichte der Honigbiene.
Franz, A., 1906. — In " Unsere Bienen," herausgegeben von Ludwig, A., Berlin.

pp. [viii]+831..
Hommell, R., 1906. — Apiculture, Encyclopedic Agricola, Paris.
Phillips, E. F., 1905. — Structure and development of the compound eye of the

bee. Proc. Acad. Nat. Sci. Philadelphia, vol. 57, pp. 123-157.
Sladen, F. W. L., 1911. — How pollen is collected by the social bees, and the
part played in the process by the auricle. British Bee Journal, vol. 39,
pp. 491-493, Dec. 14.
Sladen, F. W. L., 1912. — (a) How pollen is collected by the honey bee. Nature,
vol. 88, pp. 586, 587, Feb. 29.

1912. — (&) Further notes on how the corbicula is loaded with pollen.

British Bee Journal, vol. 40, pp. 144, 145, Apr. 11.
1912.— (c) Pollen collecting. British Bee Journal, vol. 40, pp. 164-166,

Apr. 25.
1912. — (d) How propolis is collected. Some further notes on pollen-
collecting. Gleanings in Bee Culture, vol. 40, pp. 335, 336, June 1.
1912. — (e) Hind legs of the worker honey bee. Canadian Bee Journal,
vol. 20, p. 203. July.
Wolff, O. J. B., 1873. — Das Pollen-Einsammeln der Biene. Eichstadt Bienen-
Zeitung. 29 Jahrg. Nrs. 22 u. 23, pp. 258-270.

IEDEX.

Page.

Alefeld on pollen moistening by worker bee 23

Antenna cleaner of worker bee, figure *S

Auricle of hind planta of worker bee, definition 9

figure 11

role and action in pollen collect-
ing 16-17, 19, 20-22

Basket, pollen. (See Corbicula.)

Brush of foreleg of worker bee, action and role in pollen collecting 13

figure 8

hind leg of worker bee, action and role in pollen collecting 16

middle leg of worker bee, action and role in pollen collecting 14-16

figure 9

Brushes of legs of worker bee, use in pollen collecting 8-9

Bumblebee, moistening of pollen, views of Sladen 23-24

Cheshire on process of loading pollen baskets by worker bee 17

Comb or pecten of hind tibia of worker bee, definition 9

figure 77

role and action in pollen col-
lecting 16-19

Corbicula of worker bee, definition 9

figure 10

process of loading 15-22

Corn, sweet, pollen collecting therefrom by honey bee 11-13

Coxae of worker bee, figures 8,9

Dunbar, Dr. P. B., analyses of corn pollen from plant, from corbiculse

of bees, and from hive cells 28

Femora of worker bee, figures 8, 9, 10, 11

Fleischmann and Zander on process of loading pollen baskets by worker

bee IS

Flowers, variable amounts of pollen from different plants 10-11

Franz on pollen moistening of worker bee 23

process of loading pollen baskets by worker bee 17

Hairs, branched, of honey bee, use in pollen collecting 7-8

fringing pollen basket, function 20

unbranched, of honey bee, use in pollen collecting 7, 8

Hommell on pollen moistening of worker bee 23

process of loading pollen baskets by worker bee IS

Honey, use by worker bee for moistening pollen 24, 28-29

Leg, hind, of worker bee, loaded with pollen, figure 22

Legs, fore, of worker bee, action and role in pollen collecting : 12,13

hind, of worker bee, action and role in pollen collecting 13, 16-18

stages in basket-loading process, figure 19

middle, of worker bee, action and role in pollen collecting 13, 14-16

of worker bee, action in unloading pollen 30-31

structures used in pollen collecting 7-9

35

36 BEHAVIOR OF HONEY BEE IN POLLEN COLLECTING.

Page.

Mandibles of honey bee, action and r61e in pollen collecting 8, 13

worker bee, use in packing pollen in the cell 31

Maxillae of honey bee, action and role in pollen collecting 8, 13

Moistening of pollen by bumblebee, views of Sladen 23-24

honey bee . 13, 22-29

Mouthparts of honey bee, action and role in pollen collecting 8, 13

Nectar, supposed use by worker bee for moistening pollen 24-29

Palma of foreleg of worker bee, definition 8

Pecten of hind tibia of worker bee, definition 9

figure 11

role and action in pollen collectings 16-19

Planta of hind leg of worker bee, definition 8

figures ___ 10, 11

structures concerned in pollen collect-
ing 9

middle leg of worker bee, definition 8

Pollen, chemical composition 26

collecting by worker bee, bibliography 33

general statement regarding it 11-13

summary of process 31-32

corn, from plant, from corbiculse of bees, and from hive cells,

analyses to determine nature of moistening fluid 28-29

moistening by bumblebee, views of Sladen 23-24

honey bee 22-29

storage in the hive 29-31

structures of honey bee concerned in manipulation 7-9

supply of honey bee 10-11

unloading process by worker bee 30-31

Saliva, supposed use by worker bee in moistening pollen 23,29

Sladen, observations on process of loading pollen baskets by worker

bee 18, 20, 21

views as to pollen moistening by worker bee 23-24,27

Spur of middle tibia of worker bee, figure 9

Storing pollen in the hive 29-31

Structures of honey bee concerned in manipulation of pollen 7-9

" Sweat glands " of Wolff within hind tibia and planta of worker bee,

supposed function 24

Tibia of hind leg of worker bee, modifications and structures for pollen

collecting 9

Tibiae of worker bee, figures 8, 9, 10, 11

Tongue of worker bee, action and role in pollen collecting 8, 13

Trochanters of worker bee, figures 8, 9

Wax shears or pinchers, so-called, use in loading pollen by worker bee 7

Wolff on pollen moistening by worker bee 24

Zander, Fleischmann and. (See Fleischmann and Zander.)

o